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Ligands

A ligand is an ion or small molecule that binds to a metal atom (in chemistry) or to a biomolecule (in biochemistry) to form a complex, such as the iron-cyanide coordination complex Prussian blue, or the iron-containing blood-protein haemoglobin.

Controlled switching of the spin state of transition metal ions is key in many enzymatic reactions, but difficult to replicate in synthetic systems. Here the authors report on an iron(III) porphyrin with a photochromic axial ligand that, in solution, reversibly switches between low-spin and high-spin upon irradiation with two different wavelengths.

Hyperpolarization methods play a crucial role in the in vivo observation of molecular metabolism by MRI techniques. Here, the authors develop NHC-containing iridium complexes which improve the NMR detectability of 1H, 13C and 15N nuclei via transfer of latent magnetism of para-hydrogen into a substrate.

Metal-mediated activation of CO for C-C coupling reactions is a valuable approach to carbon monoxide valorization. Here, the authors use low-coordinate iron(II) complexes for the selective scission and homologation of CO affording unusual squaraines and iron carboxylates under mild conditions.

The histidine brace found in certain copper oxidases enables the oxidation of strong C–H bonds in organic substrates. This Perspective highlights and discusses the possible structural and electronic features of this motif and how these features underlie its role in challenging oxidative catalysis.

An essential open question in functional transition metal complexes is the relative roles of charge-transfer and metal-centered excited states. Here the authors identify the important role of metal-centered excited states in the linkage photoisomerization of a photochromic Ru-sulfoxide complex.

News and Comment

Mathematically modelling metal–ligand bonding in late transition-metal complexes has been an important tool in catalyst development — although lacking for early transition metals such as Cr and Ti. Now, a simple method for measuring ligand donor properties promises to elevate high-valent early transition metal catalysis to the same level.